“There’s a pivotal scene where I’m in one of the towers, and I pick up a machinegun, and I end up firing at the enemy and ultimately end up saving this platoon,” McCartney told Yahoo! Music in an exclusive interview.

“But when I come home, something terrible happens to Tim, and he can’t get over it, and he suffers from posttraumatic stress disorder which is something a lot of our soldiers go through,” he said.

To prepare for the character, the singer and actor who will join The Backstreet Boys on their In A World Like This tour this summer, watched war documentaries “The Battle of Marjah” and “Restrepo” and spoke to actual soldiers.

Being on the show gave him a newfound respect for our troops. “[It] made you think about what these people actually go through and what they actually give,” he said.

During the interview, McCartney also shares details of his rigorous military training, including learning how to assemble a gun several times in less than one minute.

McCartney is also working on his fourth solo album, a follow up to 2008’s “Departure.”